High voltage stand-off insulator assembly in a sputter-ion vacuum pump



w. R. WHEELER Feb. 20, 1968 HIGH VOLTAGE summon INSULATOR ASSEMBLY ISPUTTER-ION VACUUM PUMP Filed Nov. 16, 1966 INVENTOR, E WILLIMLBIjEELER6; h ORNEY United States Patent Ofiice 3,369,734 Patented Feb. 20, 1968HIGH VOLTAGE STAND-OFF INSULATOR ASSEMBLY IN A SPUTTER-ION VACUUM PUMP IWilliam R. Wheeler, Saratoga, Calif., assignor to Varian Associates,Palo Alto, Calif. Filed Nov. 16, 1966, Ser. No. 594,739 8 Claims. (Cl.23069) ABSTRACT OF THE DISCLOSURE An insulator assembly for use in asputter-ion vacuum pump. The ceramic insulator element has a re-entrantportion which is shielded from sputtered getter material by an openmetal cup which is fastened to the anode and by a box-shaped bracketwhich is connected to the cathodes. By eliminaiing the formation ofgetter-metal deposits on the re-entrant portion of the insulator,eectrical breakdown across the surface of the insulator is prevented.

The present invention relates to high voltage insulators. Moreparticularly, it relates to a high voltage standoff insulator assemblywhich impedes surface electrical leakage and surface voltage breakdowncaused by sputtered material deposited on insulator members supportinghigh potential difference elements insulatingy spaced apart.

A common problem found in mounting high potential difference elementsinsulatingly spaced apart is the tendency for voltage breakdown to takeplace along the surface of the insulator members. Voltage breakdownalong the surface of insulators occurs as a result of sputtered materialbeing deposited from the high potential difference elements onto thesurface of the insulators. As material is repeatedly sputtered from thehigh potential difference elements and deposited along the surface ofthe insulator, eventually, a short circuit path is formed between theelements along the insulator surface by the deposited. sputteredmaterial. This short circuit path establishes a surface current leakagewhich eventually causes a breakdown in the potential difference betweenthe high potential difference eemeiits. Hence, electrical leakage alongthe deposited layers is undesirable.

During a gaseous discharge between high potential difference element's,material is sputtered from the negative element. It has been thepractice to employ two metal cups to shield the surface of a columnarinsulator from the sputtered material. Normally, such cups are fastenedat opposite ends of the insulator with their receptacles facing eachother to have their lips spaced apart and overlapping each other. Whensuch high voltage stand-off insulators are used in ion getter pumps, ithas been found that the pressure in the pump will be correct at sometimeduring normal pumping operations to allow a discharge between the twoshield cups. This discharge takes place in regions unshielded from thecolumnar insulator. Hence, the sputtered material liberated by thedischarge can coat the surface of the insulator to cause surface leakageand voltage breakdown.

Accordingly, it is the object of the present invention to provide a highvoltage stand-off insulator assembly which is free of surface leakageand surface voltage breakdown effects caused by material sputtered fromhigh potential difference elements.

'One feature of the present invention is the provision of a stand-offinsulator assembly including an insulator member whosesurface defines aperimetrical re-entrant portion which is effectively shielded to preventsputtered getter material from depositing therein.

Another feature of the present invention is the provision of a stand-offinsulator assembly of the above featured type wherein a cup-shapedmember defining a receptacle is mounted to receive in its receptacle theportion of the insulator defining the re-entrant so that the opening ofthe re-entrant faces the receptacle to thereby shield the entire surfaceof the insulator defining the re-entrant from the region in whichsputtering occurs.

Still another feature of the present invention is the provision of astand-off insulator assembly of the above featured types wherein thecup-shaped member is made of conductive material and is secured to oneelement of the high potential difference elements to extend through anopening defined by a conductive member secured to the other highpotential difference element, with the cup-shaped receptacle facing awayfrom the opening whereby arcing can occur between the outside surfaceportion of the cup-shaped member and the portion of the conductivemember defining the opening.

Yet another object of the present invention is the provision of astand-off insulator assembly of the above featured types wherein theterminal edge of the conductive cup-shaped member is rolled outwardly ofthe receptacle to thereby enhance the possibility of discharge occurringalong the surface of the cup-shaped member external of the receptacle.

Another feature of the present invention is the provision of a stand-offinsulator assembly of the above featured types for use in an ion gettervacuum pump to secure the pump elements thereof in insulatingly spacedapart relation.

These and other objects and features of the present invention willbecome more apparent upon consideration of the following specificationand claims in conjunction with the accompanying drawing in which:

FIG. 1 is an exploded view of one embodiment of the high voltagestand-off insulator of the present invention.

FIG. 2 is an illustration of an ion getter vacuum pumpin which the highvoltage stand-off insulator assembly of the present invention isparticularly suited for use.

FIG. 3 is an enlarged section of the pump delineated by lines 3-3 ofFIG. 2 illustrating the manner in which the high voltage stand-offinsulator assembly secures the cathode and anode elements of the pump ininsulatingly spaced apart relation.

FIG. 4 is an enlarged section of FIG. 3 taken at lines 4-4 detailing theconstruction of the high voltage stand-off insulator assembly.

With reference to FIG. 1, the high voltage stand-off insulator assembly11 of thepresent invention comprises a columnar insulator member 12,generally cylindrical and of ceramic, provided with threaded endsections 13 and 14 for securing the insulator member to spaced aparthigh potential difference elements. The outer surface of the ceramicmember 12 defines a circumferential re-entrant portion 16. Consequently,in order for sputtered material to collect on the ceramic insulator 12in such a manner as to define a conductionpath between its end sections13 and 14, sputtered materialmust enter the re-entrant portion 16. Byarranging ceramic insulator member 12 so that at least a portion of itssurface defining the re-entrant 16 is shielded from regions in whichsputtering occurs, a conduction path will not be established between theend sections 13 and ber 17 defining a receptacle 18 (see FIG. 4) ismounted to receive therein the end 13 of the ceramic insulator 12 whichthe re-entrant 16 opens towards. The depth of the receptacle 18 definedby the cup-shaped member 17 is adjusted so that the cup-shaped member 17extends past the outer lip 12 defining the re-entrant opening. With suchan arrangement, the re-entrant 16 is shielded from all line of sightpaths from the region in which sputtering occurs.

A gaseous discharge, Which sputters material, generally occurs betweenthe closest points of spaced apart high potential difference elements.To insure that the discharge does not occur between points, one of whichis along a line of sight path to re-entrant 16, the cup-shaped member 17is constructed of conductive material. In use, the cup-shaped member 17and ceramic insulator 12 at end section 13 are fastened, for example, byscrews 21, to one of a pair of high potential difference elements (seeFIG. 4), preferably, the positive potential elements. The opposite endsection 14 of the ceramic insulator 12 is similarly fastened by screws21 to the other of the pair of high potential difference elements.Therefore, since the cup-shaped member 17 is a conductive extension ofone of the high potential difference elements, and is positioned closerto the other high potential difference element than is the element towhich it is attached, the discharge that occurs will take placeproximate the terminal edge 22 of the cup-shaped member 17. As can beseen with reference FIG. 4, there is no line of sight path from theregion in which sputtering occurs, i.e., at terminal edge 22 ofcup-shaped member 17, to the reentrant 16.

It is preferred to connect the conductive cup-shaped member 17 to themore positive of the high potential difference elements because thematerial is sputtered from the negative potential element. If theconductive cupshaped member 17 is attached to the more negativepotential element, in some cases, material could be sputtered from theinner wall of web 23. Some of the material sputtered from the inner wallof web 23 would enter re-entrant 16 of the insulator 12. Such materialwould be deposited along the surface of re-entrant 16 to coat theinsulator surface and establish an undesirable conduction path betweenthe high potential difference elements.

However, when used in an ion getter vacuum pump, a considerable amountof sputtered material from the pumping elements is present and can enterand be deposited on the walls defining the receptacle 18. The moresputtered material entering the receptacle 18, the more probable thatsome sputtered material will eventually enter re-entrant 16.

With this in mind, a conductive member 26 is mounted to extend from thehigh potential difference element to be supported in spaced relationwith that high potential difference element connected to cup-shapedmember 17. The conductive member 26 includes an extension 27 defining anaperture 28 through which cup-shaped member 17 extends. The extension 27prevents sputtered material originating from the side of extension 27distal edge 22 of cup-shaped member 17 from reaching insulator 12. Toshield insulator 12 from sputtered material originating from anydirection, the conductive member 26 could be constructed in the form ofa cup-shaped member surrounding the cup-shaped member 17.

With the terminal edge 22 rolled outwardly of the receptacle 18, ittogether with the apertured extension 27 surrounding cup-shaped member17 enhance the possibility of discharge occurring. at locations alongoutwardly facing surface 24 of cup-shaped member 17. Furthermore, theconductive member 26 further shields insulator 12, hence reducing thesputtered material which can enter re-entrant 16 to an insignificantamount.

In one embodiment particularly suited for use in constructing unitaryelectrode assemblies for cellular sputter ion vacuum pumps, conductivemember 26 is box-shaped whose upper extension 27 defines two spacedapart apertures 28, each aperture 28 receiving therethrough a ceramicinsulator 12 and cup-shaped member 17 as described hereinabove. Eachceramic insulator 12 is fastened by screw 21 at its end section 14 to alower extension 29 of the box shaped conductive member 26. The upper andlower extensions 27 and 29 are joined by ribs 31. At each of the fourcorners defined by the junctions of the ribs, and the upper and lowerextensions is mounted a tap 32 for fastening a high potential differenceelement, e.g., a cathode of a sputter ion vacuum pump, to the highvoltage stand-off insulator assembly 11.

Although the cup-shaped member 17 and apertured conductive member 26have been described as separate elements mechanically fixed to differenthigh potential difference elements, it should be appreciated that thecup member 17 and apertured conductive member 26 could be formed by anintegral part of the high potential difference elements.

Referring now to FIGS. 2-4, a sputter ion vacuum pump 41 is shownemploying the high voltage stand-off insulator assembly 11 to supportthe electrodes of the pump in insulatingly spaced apart relation. Theinsulator assembly of the present invention is particularly suited foruse in an ion getter vacuum pump because of the presence of a largeamount of sputtered material. In the manner described hereinabove, thecup-shaped member 17 and conductive member 26 will shield the reentrant16 defined by the outer surface of the ceramic insulator 12 fromsputtered material from the pump ele ments if the insulator 12 andcup-shaped member 17 are positioned with the receptacle 18 defined bythe cupshaped member 17 facing away from the region of pump sputtering.

In the pump embodiment illustrated, a cellular anode assembly 42, heldtogether with a conductive band 43 tightly wound around the perimeter ofthe cells 44 forming the assembly, is fixed between cathode electrodes46 and 46' by two high voltage standoff insulator assemblies 11 todefine a unitary pump electrode assembly. More specifically, aninsulator assembly 11 having two columnar ceramic insulators 12 andconductive cup-shaped members 17 is fixed to the conductive band 43 ofthe cellular anode assembly 42 at opposite ends thereof. The conductiveband 43 is fastened by screw 21 through cup-shaped member 17 to endsection 13 of ceramic insulator 12. The opposite end section 14 ofinsulator 12 is fastened to the lower extension 29 of box-shapedconductive member 26 by screws 21. The cathode plate elements 46 and 46are fastened by screws 47 to the insulator assembly 11 at tabs 32 onopposite sides of the assembly 11.

The unitary pump electrode assembly formed by cellular anode assembly42, cathode plates 46 and 46 and two high voltage stand-off insulatorassemblies 11 are positions within the pump envelop 51 between the polesof magnet 52. Generally, the cathode plates 46 and 46 are operated atground potential with the cellular anode assembly 42 at 3-8 kv. Theanode assembly 42 is energized by coupling an external power supply (notshown) thereto through a high voltage vacuum feedthrough 53 whichinsulatingly transpierces the pump envelope 51.

During pump operations, the feedthrough insulator 54 which shields thehigh voltage lead 56 from contact with the commonly grounded envelop 51,should be shielded to prevent sputtered material originating in the pump41 from depositing on the feedthrough insulator 54. If preventive stepsare not taken to prevent such sputter material deposition, current pathsbetween the high voltage lead 56 and the grounded envelop can beestablished which lead to surface voltage breakdown. The ceramicinsulator member 12 could'be adapted to serve as a feedthrough with thecup-shaped member 17 mounted at the vacuum end thereof to shield there-entrant 16 from sputtered material. Of course, the high voltage lead56, or leads,

would pass through the ceramic insulator member 12 and cup-shaped member17.

While the present invention has been described in detail with referenceto one specific embodiment, many modifications are possible within thescope of the invention, particularly with respect to the use of the highvoltage stand-off insulator assembly in ion getter vacuum pumps tosupport the various electrodes commonly found therein, e.g., gridelectrodes in triode type pumps, and fourth electrodes in tetrode typepumps. Hence, the present invention is not intended to be limited exceptby the terms of the following claims.

What is claimed is:

1. A high voltage stand-off insulator assembly comprising a columnarinsulator member having an outer surface defining a perimetricalre-entrant portion, a cup-shaped member defining a receptacle fixedlypositioned and receiving said columnar insulator in said receptacle withthe re-entrant facing said receptacle, and a conductive member mountedinsulatingly spaced apart from said cupshaped member, said conductivemember defining an aperture through which said insulator and cup-shapedmembers extend.

2. The high voltage stand-01f insulator assembly according to claim 1wherein said cup-shaped member is of conductive material and is securedto the more positive of two high potential difference structures, saidconductive member is secured to the less positive of said two highpotential difference structures, and said columnar insulator is securedto each of the high potential difference structures at its opposingends.

3. The high voltage stand-off insulator assembly according to claim 2wherein said cup-shaped member has an outwardly rolled terminal edgeabout the opening of the receptacle defined thereby.

4. The high voltage stand-off insulator assembly according to claim 2wherein said columnar insulator member is cylindrical having acylindrical re-entrant portion circumferentially about said cylindricalmember, said cupshaped member is a cylinder having one open end, andsaid conductive member has a first extension having said aperturetherein and a second extension joined by rib means to said firstextension in spaced side-by-side relation to said first extension, theend of said insulator member opposite said cup-shaped member beingsecured to said second extension.

5. The high voltage stand-01f insulator assembly according to claim 1wherein said conductive member has a first extension means and secondextension means joined thereto by rib means in spaced side-by-siderelation to define a box-shaped conductive member, said first extensionmeans having said aperture and a second aperture therethrough, saidcup-shaped and columnar insulator members extending through one of saidapertures with the end of said columnar insulator member facing oppositesaid re-entrant portion fixed to said second extension means, andfurther including a second columnar insulator member having an outersurface defining a circumferential re-entrant portion fixed to saidsecond extension means at its end facing opposite said re-entrantportion and extending through the other of said apertures, and a secondcup-shaped member defining a receptacle fixedly positioned and receivingsaid second columnar insulator in said receptacle with the re-entrantfacing said receptacle and extending through said other aperture, andmounting means to secure a first of high potential difierence electrodesto an edge of said conductive member defined by said first and secondextension means and to secure a second of said high potential differenceelectrodes to the ends of said insulators fixed to said cup-shapedmembers.

6. In a sputter ion vacuum pump including an evacuable envelope forenclosing the pumping elements and a magnet means for establishing amagnetic field for elongating the path of ionizing electrons, an anodeelectrode, and at least a second electrode means serving with said anodeto define a sputter region therebetween, and a high voltage stand-0Einsulator assembly fixing said second electrode insulatingly spaced fromsaid anode electrode including a columnar insulator member having anouter surface defining a perimetrical re-entrant portion, and cupshapedmember defining a receptacle fixedly secured to an end of said insulatormembers and receiving said insulator member in said receptacle with there-entrant facing said receptacle, the improvement therein being thatthe end of said insulator fixed to said cup-shaped member is secured toone of said electrodes to have the receptacle defined by said cup-shapedmember facing away from said sputter region, the other end of saidinsulator being secured to the other electrode to hold said electrodesinsulatingly spaced from each other.

7. The apparatus according to claim 6 further including a conductivemember fixed to said electrode secured to the end of said insulatormember opposite the cupshaped member, said conductive member defining atleast one aperture through which said insulator and cup-shaped membersextend, said cup-shaped member being insulatingly spaced from saidconductive member.

8. In a sputter ion vacuum pump having an anode electrode, at least asecond electrode means serving with said anode to define a sputterregion therebetween, and a high voltage stand-off insulator assembly forinsulating said second electrode from said anode electrode including acolumnar insulator member having an outer surface defining aperimetrical re-entrant portion and a cup-shaped member defining areceptacle fixedly secured to one end of said insulator member andreceiving a portion of said insulator member in said receptacle with there-entrant facing said receptacle, said one end of said insulator beingsecured to one of said electrodes, the improvement therein comprising aconductive member defining at least one aperture through which saidinsulator and cup-shaped members extend, the other end of said insulatorbeing fixed to said conductive member, said cup-shaped member beinginsulatingly spaced from said conductive member, and the other of saidelectrodes being fixed to said conductive member to space said other ofsaid electrodes from said anode electrode.

References Cited UNITED STATES PATENTS 1,146,298 7/1915 Ambruster l74l381,481,081 1/1924 Austin l74140 2,550,367 4/195 1 Meier 174-138 X3,115,297 12/1963 Lloyd et a1. l74l38 X 3,228,590 1/1966 Kearns et a1230-69 LARAMIE E. ASKIN, Primary Examiner.

